IS 7784 (Part 21Sec 5) : 2000 smrftzT "lfF1C1) ~..xm: ~ f~Cf)I;g ~ t' f-$\il1~1 'Ufu ~ \111T 2 n-~Iee ~ ~ 5 lIll'F' l{~)iqc: (Wffl~~) "'\ Indian Standard CODE OF PRACTICE FOR DE.ON OF CROSS DRAINAGE WORKS PART2 SPECIFIC REQUIREMENTS Section 5 Syphon Aqueducts (First Revision) ICS 93.160 ©BIS 2000 BUREAU OF INDIAN STANDARDS MANAK BHAVAN, 9 BAHADURSHAH ZAFAR MARG NEW DELHI 110002 October 2000 Price Group 5 AMENDMENT NO. 1 AUGUST 2005 TO IS 7784 ( PART 2/SEC 5 ) : 2000 CODE OF PRACTICE FOR DESIGN OF CROSS DRAINAGE WORKS PART 2 SPECIFIC REQUIREMENTS Section 5 Syphon Aqueducts (rnt RnI&io") (Page 1, clause 2 ) - Substitute the following for the existingmatter: 'The following standards contain provisions which through reference in this text, constitute provisions of this standard. At the time of publication, the editionsindicated werevalid. All standards are subjectto revision, and parties to agreements based on this standard are encouraged to investigate the possibility of applyingthe mostrecenteditionsof the standards indicated below: IS No. IS 269 : 1989 Tille Specification for 33 grade ordinary Portland cement (fourth revision) IS 455: 1989 IS 456: 2000 Specification for Portland slag cement Plain and reinforced concrete- Codeof practice (fourth revision) IS 1077: 1992 IS 1489(Part 1 ) : 1991 Common buml claybuildingbricks- Specification (fifth revision) Specification for Portland pozzolana cement: Part I Flyashbased Specification for Portland pozzolana cement : Part 2 Calcined clay based IS 1489( Part 2) : 1991 IS 2116: 1980 Specification for sand for masonry mortars Glossary of teons relatingto river valley projects: Part 15 Canal structure, Section 5 Cross drainage works (first revision) IS 4410 (Part 15/ Sec 5): 1992 Cross Drainage Works Sectional Comnuttee, WRD 17 FOREWORD ThisIndian Standard (Part2/Sec draftfinalized by theCross Oral Divisron Council IS 7784 hasbeen published m tv cross dramage works Part 2 ( sections Section Section Section Section Section I Amend No. 1 to IS 7784 ( Part 2ISee 5 ) : 2000 ISNo. IS 7779 : 1975 Titl, Schedule for properties aod availability of stones for const1Uction purposes IS 7784 ( Part 1): Code of practice for design of cross drainage works : Part1 1993 General features (first milion) IS IS 7784 (Part 21 Code ofpractice fordesign of cross drainage works : Part 2 Sec 1)' 1995 Specific requirements, Section 1 Aqueducts (jIrst MIlston) 2 3 4 5 Aqueducts Superpassages Canal syphons Level crossings Syphon aquedi IS 7894 : 1975 IS 8112 : 1989 Code of practice for stability analYSIS of earth dams Specification for 43 grade ordinary Portland cement Code of practice for protection of slope for reservoir embankment (first revision) Thisstandard (Part2/Sec 5) cow Thivstandard wasfirst pubhshed of thestandard, which lays dowi have been effected in Part1of tI M) IS 8237 . 1985 IS 8605 : 1977 IS 12894 : 2002 Codeof practicefor construction of masonry in dams Specification forflyash lime bricks as to align thesame With Part There l'i noISOstandard on the· data/practices pravalent m the fi Forthepurpose of deciding whe observed or calculated expressi IS2 1960 'Rule'i forrounding 0 rounded off value should he the 13757 . 1993 Specification for burntclayflyash building bricks (Page 1,subclause S.2.1 ) - Insert thefollowing subclause after S.2.1. 'S.2.2 In respect of masonry, m addition to common burnt clay building bricks confonning to IS 1077 andstones confonning to IS 7779 or IS 860S, pulverized fuel ash-lime bricks confonning to IS 12894 and burnt clay tlyash buildmg bricks confonning to IS 13757 shall be used. For masonry mortar, cement confonning to IS 269 or IS 8112 or IS 45S or IS 1489 (Part 1) or IS 1489 (part 2) shall be used. Sand formasonry mortar shall conform to IS2116.' (WRD 13) Roprosraphy Unit, BIS, NewDelhi, India 2 Cross Drainage Works Sectional Committee, WRD 17 FOREWORD Thrs Indian Standard (Part 2/Sel. 5) (Flr~t Revision) was adopted by the Bureau of Indian Standards, after the draft finalued by the Cross Drainage Works Sectional Comrmttee had been approved by the Water Resources DIV1\IOn Council 1'\ 7784 has been published crow dramage works In two parts Part 1 of this standard covers general requirements of the design of Part 2 covers specific requirements and has been pubhshed In the following five sections Section 1 Section 2 Section 1 Aqueducts Superpassages Section 4 Section 5 Canal syphons Level crossings Syphon aqueducts 1 hl\ standard (Part 2/Se(,. 5) covers specific design requirement, tor syphon aqueducts This standard Wei, first published In the year 1980 This revision was taken up 10 view of the rCVIMon of Part I of thc standard, which lays down general requirements for design of cross drainage works As modificanons have been ettectcd In Part I of the standard, this revisron I~ intended to modify the provisrons ot this standard vo d\ to align the same With Part I I here 1\ no I~O standard on the subject This standard has been prepared based on indigenous manufacturers' d,lt,vprdl.tIl.C\ pravalent In the field 10 India For the purpose of decidmg whether a particular requirement of this standard IS complied With, the hnal value, observed or calculated expressing the result of a test or ,1O,1IyM\, shall be rounded off 10 accordance With I~ 2 1960 Rules for rounding off nurnencal value, (revised)' The number of significant places retamed 10 the rounded ott value should be the same a\ that of the specined value 10 this standard IS 7784 (Part 2/Sec 5) : 1000 Indian Standard CODE OF PRACTICE FOR DESIGN OF CROSS DRAINAGE WORKS PART 2 SPECIFIC REQUIREMENTS Section 5 Syphon AqUedUcts (First Revision) 1 SCOPE This standard (Part 2/Sec 5) lays down specific design requirements for syphon aqueducts 2 REFERENCES The following standards contain provrsions which through reference in this text, constitute provisions of this standard At the time of publication, the ediuons Indicated were valid All standards are subject to revrsion, and parties to agreements based on this standard are encouraged to Investigate the possibrhty of applying the most recent editions of the standards mdu.ated below IS No TItle rectangular, horse shoe shape, SIngle or multi cell barrels can be adopted 5.1.2 Precast RCC pipes may be economical for syphonmg small drainage discharges For large drainage discharges, circular, square, rectangular or horse shoe shaped barrels are surtable Rectangular section may be preferable due to ease of construction and mamtenance 5 2 Materials 5.2.1 For the construction of the syphon barrels, prestressed concrete, RCC or masonry or a combmauon of these may be used dependmg upon the availabrhty of materials, labour and relative economy 6 TYPES OF SYPHON AQUEDUCTS 456 1978 Code of practice for plain and reinforced concrete (third revtsiont Glossary of terms relatmg to nver valley projects Part 15 Canal structure, Sec 5 Cross drainage work (first revistoni 4410(Part 15/Sec 5) 1992 7784(Part l) 1991 Code of practice for design of cross drainage works Part I General features (first revision) 6.1 Syphon aqueducts may be classified Into the following two types a) Barrel type, USIng barrel for drainage waterways, and b) Trough type, using trough section for carrier channel waterways 6.2 In barrel type of syphon aqueducts, the entire earner channel portion may be taken as It ISover the barrel or It may be flumed to a rectangular or trapezoidal section to reduce the length of barrels (see Fig lA, IB and IC) 6.3 In trough type of syphon aqueducts, camer channel Water IS taken across drainage channel through a trough supported on barrels or on piers/abutments raised from the drainage bed (see FIg ID, IE and IF) Bottom of the trough of carrier channel I~ lower than HFL of drainage channel An ImperVIOUS floor, If necessary, WIth protection against surface and sub surface flow may be provided 10 drainage bed 6.4 It IS preferable to regrade the exit of drainage channel or stream to allow the water to flow without restraint If It ISeconomically feasible When It ISnot feasible, the bed may be regraded to a SUitableslope The type of syphon aqueduct to be adopted shall be decided on the basis of relative economy and restramts of earner channel design 10751 1994 Planning and design of guide banks for alluvial river Guidelmes (first revtstoni 3 TERMINOLOGY For the purpose of this standard, the defimtions given In IS 4410 (Part I5/Sec 5) shall apply 4 DATA FOR DESIGN For the design of syphon aqueduct, data given In I~ 7784 (Part 1) shall be made available In addition, value of ·n' for the design of drainage channel shall be known 5 GENERAL DESIGN CONSIDERATION 5.1 Shape 5.1.1 For desigmng syphon aqueduct, circular, square, IS 7784 (Part 1/Sec 5) : 2000 7 LAYOUT 7.1 General 7.1.1 The layout of syphon aqueduct shall be so fixed that the drainage channel crosses the earner channel preferably at TIght angles 7.2 7.2.6 The length of barrels should be fixed on the considerauon of economics of Increasing barrel length With respect to reduction In length of wmg walls of drainage channel and height of breast wall and practical and economical depth ofcut off under barrels for safe exit gradient However the length should be sufficient to accommodate the Width of service road Barrel 7.3 Drainage Wings 7.3.1 The length of drainage wings shall be adjusted so as to contain the slopes of carrrer channel embankments The wings shall be provided straight or 10 a smooth curve giving a minimum splay of 2 1 on upstream and 3 1 on downstream If necessary, return wall may be provided thereafter The top of wings shall be kept at least 300 mm higher than the HFL of the dramage channel 7.2.1 The floor level of barrels shall be fixed 10 relanon to the drainage bed level at the syphon aqueduct site The future retrogression and regrading of drainage channel depending on outfall conditions may also be considered The floor level IS combination with vent way shall be judiciously fixed below the existing dramage bed In such a manner that a water seal of 1 5 times the change m velocity head, With a minimum of 150 mm, should be provided over the crown of barrels at start to prevent air entenng the barrel 7.2.2 At the outlet end of the syphon, the top of the barrel may be kept shghtly depressed below the normal downstream flood level 10 the drainage channel The amount of this depression may be equal to the difference In the velocity head at the exrt end of the barrel and that In the drainage channel on the downstream SIde 7.2.3 In case of barrel of R C C box type or R C C slab with masonry walls, a mimmum cushion of lOO rnrn may be provided With the precaution that heavy vehicles do not ply over the barrels unless the cover IS vurtably Increased and the structure IS properly designed In case of R C C pipes and circular barrels, a mmimum cushion of 900 mm should be provided This Will protect the pipes and barrels against damage by the movement of construction equipment over them This cover also permits any future regrading of the carrier channel 7.2.4 At the site of syphon aqueduct the drainage bed I~ generally depressed and provided WithPUCCA floor (Fig I E) On the upstream Side, the dramage bed may be JOined to the PUCCA floor by a vertical drop (when drop I~ of the order of I m or less) or by a glacis of l 1 (when drop ISmore then 1 m) The downstream nsmg slope should not be steeper than 5 I 7.2.5 Depending upon the bed level of earner channel and HFL of drainage channel, the barrels under the earner channel bed portion are generally lower than the barrels at the entry and exu This difference IS negotiated WIth the prOVISIon of sloping length of barrels under earner channel banks The upward mclmation of the barrel shall start from a point at least 10m away from the end of the earner channel bed Width on either Side 7.3.2 The wing wall sections shall be checked for carrier channel full and drainage channel dry condition, consrdenng backfill as saturated No passive resistance shall be considered from dramage channel Side 7.3.3 If the foundation of wing wall requires to be taken deeper than 1 5m from consideration of scour, a concrete cut-off of required depth shall be provided along the upstream face of the wing wall 7.4 Trough 7.4.1 In the case of trough type syphon aqueduct, both earner channel transiuons and drainage wings shall be provided 7.5 Carrier Channel Section and its Fluming 7.5.1 Carner Channel Section The earner channel embankment adjommg the syphon aqueduct should have adequate provisions to aVOId possibihty of any breach and to mmimize seepage The outer slope of bank should have a clear cover of 600 to 900 mm over the designed phreatic hne often referred to as hydraulic gradient, (see IS 7894 for details) High banks (say, more than 6 m height above ground level) should be checked for slope stabihty and normal provisions of filter and rock toe should be made In cases where HFL In the drainage channel IS substantially higher than bed of the earner channel, the bank of the earner channel should be checked for the condition when drainage channel IS an high floods and the carrier channel ISdry 7.5.2 Fluming Flummg ratio shall be adopted as given In IS 7784 (Part 1) keeping 10 view the permissible head loss In the camer channel, and whether the earner channel IS hned or unlined 2 IS 7784 (part 2/Sec 5) : 2000 7.5.3 Transutons The tlumed portion of the trough shall be joined with the normal section with proper transitions to minimize head loss at entry and exit The loss of head 10 transitions shall be calculated In accordance with IS 7784 (Part 1) The transitions should correspond to a muumum splay of 2 I on the upstream Side and 1 I on the downstream Side It should be ensured that the flow follows the boundaries of the Wings the Junction of RCC barrels WIth transition walls 7.6.2 In case of syphon barrels resung on compressible SOils, collars encirchng the plain joint (see FIg 2) shall be provided This Will protect the water stop from vertical shear due to excessive settlement The WIdth and thickness of collars shall not be less than 100 mm In case of syphons of multiple barrels of more than one unit, the collars shall be designed to be flexible 7.6 Joints 7.6.1 In case of RCC barrels, JOints with water stops shall be provided across and along the barrel length The maximum spacing of these JOInts In either cirecuon shall be 20 m A gap of 10 to 15 mm With water stops at all the JOints across and along the barrel should be provided The POSitionand details of joints shall be In accordance With the provisions of IS 7784 (Part t) In case of multi-barrel syphons, umts of 1 or 4 barrels can be adopted SIde by Side With longitudmal jomts between the units having water stops all around Water stops shall also be provided at 7.7 A typical layout of barrels of syphon aqueduct IS shown In FIg 1 8 LIMITING VELOCITY AND LOSS OF HEAD 8.1 Limiting Velocity The vertical slope on approaches should not be steeper than 1 In 1 on the entry Side and 1 In 4 on the exit side The rmmmum perrmssible velocity allowed m the drainage channel may be denved from Table 1 However, the velocity In the barrels shall not exceed the maximum permissrble velocity given In IS 7784 (Part 1) Table 1 Minimum Permisible Mean Velocities for Loose Granular Bed Material Material Diameter of Particle d ID Mintmum Mean Velocity Case of Depth (h 1m) VI m1s = mm (I) (2) 200 ) ~O 1~0 (1) 1911 1127 2724 24 19 19 J 4 14 12 12·10 1008 0806 Very coarse grave) 100 Coarse gravel 100 7.., 7~ -;0 ~O 2~ 2~ 1-; 1~ 10 10 ~ Cobble Coarse sand Fine sand Very fine sand Silt -; 2 2 0 ~ 0604 0402-; O~OI 01002 002 002 o 2~ 020 () 200 I iii IS 7784 (Part 2/See 5) : 2000 Correction coefficients formula V-av I where V refers to the permissible mmunummean velocity The mmimum factor of safety against uphft should be I 2 10 all the three conditions NOTE - full hydrostatiC head from camer channel full supply level to the dralnaae barrel foundation should be taken for checkang the stability Depth, Correction Coefficient, a m 0, 06 10 15 080 090 100 110 1 15 9.1.2 The bottom slab of barrel may be SUItably projected beyond Its SIde walls to take advantage of the weight of the earth wedge over the projection In counteractmg the uphft forces 9.1.3 If the weight IS taken to counteract uplift 10 design computation, the earth cushion over the barrels should not be allowed to fall below the corresponding design depth In such cases the earner channel bed should be adequately protected against erosion by providing a suitable protective cover over the earth extending 20 m upstream and downstream of the syphon Lean concrete/random rubble masonry over the barrel as addinonal weight may be provided 9.2 Safety against Internal and External Forces 20 25 120 125 10 8.2 Loss of Head The loss of head at the entry, at the exit and 10 the barrel due to fncnon and due to elbow and joints shall he calculated 10 accordance With IS 7784 (Part 1) The water way shall be so adjusted that the afflux does not exceed the hrruts of submergence tolerances of the environments 9.2.1 General The barrels should be designed strong enough for the dead load of the structure, earth and water loads, earth and water pressures, sod reaction and uplift pressure and live load, If any The combmanon of loads which WIll result 10 maximum stresses shall be carefully considered Due to the diference 10 loading, the length of barrels of major structures can be divrded mto two portions, one under carrier channel bed and the other under carrier channel banks for economical design 9 DFSIGN OF BARREL TYPE SYPHON AQUEDUCT 9.0 The main considerations for design of syphon barrels are the following a) h) c) d) It should be safe against uphft, It should be strong to resist Internal and ex ternal forces, It should be safe agamst subsurface flow, and 9.2.2 Transverse AnalYSIS The barrels for the purpose of transverse analysis shall be treated as a box The box shall be analyzed by any standard method for the following condrtions and loadings to deterrrune the worst moments, shear and thrust at any section Condinon - I Carner channel at full supply level and barrels dry (for loadmg see 9.2.2.1) Condinon - II Carner channel dry and the drainage channel at designed HFL (Including afflux) (for 1000mg see 9.2.2.2) 9.2.2.1 Loading and forces under condmon-I are as given below a) Barrel under earner channel bed portion 1) The bottom slab Will be subjected to the It should be sate against surface flow 9.1 Safety Against Uplift 9.1.1 The barrels shall have enough load to resist upward buoyancy force tend 109 to hft It The barrels underneath earner channel bed are cnncal for checking agamst uphft The safety of barrels should be checked for the tollowing three conditions a) Carner channel at full supply level and drainage barrels empty, h) The drainage channel at designed flood level and earner channel empty, and c) Carner channel IS suddenly closed and dram age barrel ISempty thereby causmg twoth irds of the head corresponding to earner channel full supply level to act Lesser percentage of head up to one-third of total head may be considered 10 case the carrier channel section IS made of relatively permeable rnaterial upward sod reaction due to entire vertical loads The SOil reaction can be assumed to be uniformly drstnbuted Uplift pressure due to subsoil water level, If any, shall also be considered, 4 IS 7784 (Part 2/Sec S) : 2000 2) The top slab will be subjected to downward loads due to earner channel water load, self weight of slab and weight of earth and hnmg, etc, over top slab, 3) The end walls Will be subjected to submerged earthpressure and water pressure corresponding to earner channel full supply level, and 10 the joint correspond 109 to HFL or no water pressure In the joint 9.2.2.4 Adequate reinforcement corresponding to worst moments and forces at different sections shall be provided 9.2.3 When RCC pipes are used In place of barrels, they shall rest on cement concrete cradle ofM 15 grade (see IS 456), which shall be SUitablyincreased at joints Standard JOInts shall be used and these shall be properly grouted to make them water tight At bends, anchor blocks shall be provided to receive the end of pipes Generally RCC pipes may be provided up to 3 cumecs discharge and rmrurnum diameter of pipe shall be 09m 4) The Intermediate or partition walls In case of multicell barrel Will be subjected to direct compression due to vertical downward loads These walls are not subject to any Significant lateral pressure when all the barrel openings are running However, these walls will also be checked for the condmon when one barrel IS dewatered for repairs and adjoinmg barrel IS filled With water and Silted up to half the height of the barrel b) Barrel under earner channel bank portion 9.2.4 Longuudtnal Analysts 9.2.4.1 Longrtudmal analysis shall be made 10 cases where loose soil or various types of ~011s are met With at the completed final level of foundation 9.2.4.2 In case the socket and spigot arrangement of collars I~ provided, the vertical displacement ot one unit Will cause extra loads and stresses on the other urut due to the restrarmng effect of the collar For analysis of these loads the barrels In longitudinal direcuon shall be considered as beams resting on elastic foundations The analysis should be carried out according to the pnnciples given by M Hetenyi ('Beams on elastic toundauon', MIs Cushing Malloy, USA) or any other standard method of analysis 9.2.4.3 The restraining force of collar can be determined by evaluating the detecuon of the two umts at the joint The collar shall be designed for the cantilever moment due to this force 9.2.4.4 The bending moment In the barrel In longitudmal direction due to supenmposed loads as well as collar reaction shall be calculated as per standard expressions for ditterent loading condiuons given by M Hetenyi and the required reinforcement shall be provided, subject to a rmrnmum nominal reinforcement In accordance WIth IS 456 9.3 Safety Against Sub Surface Flow The different members Will be subjected to the loads as enumerated above except that the carrier channel water load Will be replaced by earth load The saturation level for the earthhll may be properly accounted for With appropnate hydrauhc gradient - lme trom F S L of the earner channel WIth regard to type of SOIl compnsmg the banks Addinonal live load on service road, If any, shall also be considered 9.2.2.2 Loading and forces under condinon-Il are as given below a) Barrel under earner channel bed portion I) 2) The bottom slab WIll be subjected to upward load as for condition-I ['tee 9.2.2.1(a), (I)] The top slab Will be subjected to upward pressure correspondmg to HFL In the drainage channel and downward loads of earner channel hrung, earth frlhng and self weight 1) The mtermediate walls Will be subjected to direct tension due to net upward pressure on top slab 4) The end walls WIll be subjected to water pressure corresponding to HFL from inside and saturated earth pressure from outside b) Barrel under earner channel bank poruon due to the predommant effect of bank load the difterent members m this condition Will be subjected to loads srrmlar In nature but lesser In magnitude as compared to condrtion-I [see 9.2.2.1(b)] As such, normally, analysis for condition II In bank portions IS not required 9.2.2.3 In case of two or more monoliths each consisting of 1 or 4 barrels, the side wall of each monolith at joints shall be subjected to water pressure 9.3.1 Cut offs The depths of cut-off shall be calculated from scour and exu gradient considerations 9.3.1.1 The normal scour depth shall be computed tor the drainage channel In accordance With IS 7784 (Part I) Depth of cut oft below the entrance and exrt ends of barrels may be provided along the Width ot the barrels and along the fiver or the drainage channel wrngs up to I 25 to I ) turu,v the normal scour depth" helow HFL based on the vite condiuons In case ot IS 7784 (Part l/See 5) : 1000 rocks, the cut off shall be taken mmimum 10m from the sill of the barrel mto the fresh rock The width of concrete cut off shall not be less than 0 " m shall besUitably designed for the uplift pressuresacbng on It, according to condiuons given In '.12. 9.3.1.2 Depth of cut off shall be checked for safe exist gradient In accordance with Khosla's theory for two dimensional flow In syphons of carrying capacity over 20 cumecs the effect of" - dimensional seepage now on exu gradient shall be considered For this, electrical analogy model testing should be carried out and cut offs at the end of the barrels should be provided accordingly The safe value of exit gradient for different types of soil generally adopted can be as follows Clay Shmgle Coarse sand Fme sand 11 ADDmONAL PROVISIONS 11.1 The outer slopes of camer channel banks and drainage channel slope should be protected In the vicimty of syphon aqueduct by pitching For large Size drainage channel, properly designed guide banks should be provided 11.2 In major syphon aqueducts stop-log grooves In the barrels at the upstream and downstream ends may be provided by extending the partition walls to facihtate isolanng one or more barrels for annual repairs and maintenance Stabihty of barrels shall be suitably ensured In this case 1104 1 m 4 to 5 1105 t06 Im6t07 9.3.1.3 The vertical cut off shall also be provided under river or dramage channel wings However, the depth of cut off may be suitably reduced under wings depending upon the length of wings, but should be adequate from scour consideranons 9.3.2 Ribs at suitable spacmgs may be provided to mcrease the seepage path 9.3.3 Filter A suitable filter under open jointed cement concrete blocks or rubble should be provided along the cutoff that IS ul« of upstream cut-off and dIs of downstream cut ott The length of filter to be provided should be I 5 times the, scour depth (below drainage bed) Typical arrangement shown 10Fig "may be adopted The frlter should be designed In accordance With standard cntena conformmg to IS 8217 11.3 A retammg wall should be constructed over the barrels to retam the carrier channel banks slopes over the barrels If constructed In reinforced cement concrete, this walls (breast wall) should be constructed monohthically With the top slab of the barrels Adequate anchorage of reinforcement as well as reinforcement for proper transference of loads and moments to the top slab shall be provided The effect of live load, wherever applicable shall also be considered an the design of this wall At the Junction of this wall With barrel, a haunch of SUitable Size shall be provided 11.4 The design of the wmgs, both for earner channel and the drainage channel, shall be carried out for earth and water pressures calculated according to standard practice The effect of live load and surcharged effect, If any, shall be taken mto account while desigmng the wmgs Wmg walls shall be checked for earthquake condinons also, 10 seisnuc zones 11.4.1 Weep holes shall be provided an the drainage wmgs above low water level at spacing of 25m clc bothways In staggered fashion FIlters shall be provided at the rear end of weep holes to prevent movement of the backfill material 11.5 In case of barrels, the top slab at entry of drainage may be given a smooth curve shape to reduce afflux 9.3.3.1 The safety of filter should also be checked against heave In accordance With the method suggested by Tcrzaghi 9.4 Scour shall be considered at entry and exit of syphon barrels 10 accordance With IS 7784 (Part 1) and launching appron adequate to provide a cover of o 6 to 0 9 m over the enure slope of the scour shall be provided 10 DESIGN OF TROUGH TYPE SYPHON AQUEDUCT The basic design features of this type shall be the same a~ those ot aqueducts [see IS 7784 (Part 2/Sec 1)] However, the earner channel trough m this type should be designed so as to provide the dead load of the trough at least I 2 times the upward thrust acting on It when the drainage channel IS 10 high floods and the earner channel is dry If It IS not so, the trough shall be suitably anchored to the piers The floor of the syphon aqueduct 11.6 In case of streams In bouldery region, provision ot weanng coat 10 the floors of the barrel may be necessary 11.7 In case of multibarrels, mtermediate partition walls need to be provided With SUitable cut and ease water The mimmum thickness of the R C C walls shall be 200 mm Reinforcement In these walls shall be anchored Withthe slabs In case of RCC walls, SUitable haunches In square or rectangular barrels With haunch remforcement shall also be provided IS 7784 (Part 2/Sec 5) : 2000 PULL WATeR SUPPLY RISS NA fUR A L SURFACE LEVEL T X x UPSTREAM CUT-OFF WEEP HOLES WITH INVERTED FILTER SECTION X X 1C PULL SUPPLY LavaL 10 1E 7 IS 7784 (Part 2/See 5) : 2000 x x MAXIMUM FLOOD LEVEL STREAM FLOW _ UPSTREAM CUT-OFF DOWNSTREAM CUT-OFF SECTION XX IF FIG. I TyPES OF SYPHON AQUFDucrs 10 mm GAP TO BE FILLED WITH TARFELT LAID OVER TWO COATS OF HOT BITUMEN 20 mrn VERTICAL GAP TO BE FILLED WITH BITUMEN CAKE All drmensions In rrulhrnetres " =Thickness of top slab. and '2 = Thickness of bottom slab FIG. 2 DETAn..s OF COLLAR 8 IS 7784 (Part 2/Sec 5) : 2000 PERVIOUS PROTEen N ON FILTER SYMMETRICAL ABOUT «i TYPICAL L-SECTION OF SYPHON AQUEDUCT SECTION BB r B A-j z ~ 0.. JOINT BETWEEN MONOLITHS JOINT \ ACROSS BARREL LENGTH